The goal of this randomised controlled trial is to compare the success of two types of hip replacement in patients with hip arthritis. The main question it aims to answer is whether a new type of hip replacement (called a hip resurfacing) can be as successful as an existing hip replacement (called a total hip replacement). Patients will be given either the new hip resurfacing or the existing total hip replacement and researchers will compare their function, complication rate and physical activity.

The H1 Implant is a cementless, ceramic hip resurfacing arthroplasty (HRA) device. The intended purpose of the H1 Implant is to provide an artificial substitute for a disease-damaged hip joint to replace the articulating surfaces of the hip while preserving the underlying femoral head and natural femoral neck. This is standard for a resurfacing hip prosthesis. This study will randomise patients to receive either The H1 Implant or a primary cementless ceramic-on-poly or ceramic-on-ceramic total hip replacement (THR). Composite clinical success (CCS) scores, physical activity levels and patient reported outcome measures (PROMs) will be compared for the two groups. The primary objective of the study is to determine whether the H1 Implant is non-inferior to cementless THR in terms of CCS. The key secondary objective is to determine whether the H1 Implant is superior compared to cementless THR in terms of physical activity and PROMs. Other secondary objectives are to compare the H1 Implant and THR with respect to: safety, through collection of all device-related, operative site-related and systemic adverse events; and noise generation, through patient survey.

Inclusion Criteria:

• Patient requires unilateral primary hip arthroplasty due to primary osteoarthritis, osteoarthritis secondary to e.g. trauma, avascular necrosis or developmental hip dysplasia, or inflammatory arthritis.
• Patient is willing to comply with study requirements.
• Patient plans to be available through 10 years postoperative follow-up.

Exclusion Criteria:

• Patient has a BMI greater than 40 kg/m².
• Patient has active infection or sepsis (treated or untreated).
• Patient has insufficient bone stock at the hip (>1/3 necrosis of the femoral head or large and multiple cysts) or in general as in severe osteopenia or osteoporosis (t-score < -2.5 as measured with BMD).
• Patient is not skeletally mature.
• Patient meets the contraindication criteria of the control device.
• Patient already has another lower limb arthroplasty or arthrodesis or will require a further lower limb arthroplasty or arthrodesis within the subsequent 2 years.
• Patient lacks capacity to consent.
• Patient is unable to understand the native language of the country where their procedure is taking place

The patients, clinical assessors and data analysts will be blinded to the intervention each patient has received for the 24 month post-operative period. The surgeon, operating theatre team, radiographic analysts and CRO cannot be blinded but will not be involved in the care of the patient after the intervention unless the patient requires revision surgery.